Determining track capacity in blocks per track is fiendishly complicated.
Given an input BLOCK LENGTH and KEY LENGTH, the track capacity for a 3390 is:
TRACK CAPACITY = 1729/SPACE {rounded down}
SPACE = C + K + D
C = 10
K = KEY LENGTH FACTOR (0 IF KL=0, 8 FOR PDS DIR)
9 + ((KL + (6 * KN) + 6) / 34) {rounded up}
KL = KEY LENGTH
KN = (KL + 6) / 232 {rounded up}
D = DATA LENGTH FACTOR:
9 + ((DL + (6 * DN) + 6) / 34) {rounded up}
DL = BLOCK LENGTH
DN = (DL + 6) / 232 {rounded up}
For a 3380 is:
TRACK CAPACITY = 1499/SPACE {rounded down}
SPACE = C + K + D
C = 15
K = KEY LENGTH FACTOR (0 IF KL=0, 8 FOR PDS DIR)
7 + ((KL + 12) / 32) {rounded up}
KL = KEY LENGTH
D = DATA LENGTH FACTOR:
(DL + 12) / 32 {rounded up}
DL = BLOCK LENGTH
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